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<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="register_callback.html" title="cpp/io/ios base/register callback"><span class="t-lines"><span>ios_base::register_callback</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="sync_with_stdio.html" title="cpp/io/ios base/sync with stdio"><span class="t-lines"><span>ios_base::sync_with_stdio</span></span></a></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> 成员类</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="failure.html" title="cpp/io/ios base/failure"><span class="t-lines"><span>ios_base::failure</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="Init.html" title="cpp/io/ios base/Init"><span class="t-lines"><span>ios_base::Init</span></span></a></div></div></td></tr>
<tr class="t-nv-h1"><td colspan="5"> 成员类型</td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="openmode.html" title="cpp/io/ios base/openmode"><span class="t-lines"><span>ios_base::openmode</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="fmtflags.html" title="cpp/io/ios base/fmtflags"><span class="t-lines"><span>ios_base::fmtflags</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="iostate.html" title="cpp/io/ios base/iostate"><span class="t-lines"><span>ios_base::iostate</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="seekdir.html" title="cpp/io/ios base/seekdir"><span class="t-lines"><span>ios_base::seekdir</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="event.html" title="cpp/io/ios base/event"><span class="t-lines"><span>ios_base::event</span></span></a></div></div></td></tr>
<tr class="t-nv"><td colspan="5"><div class="t-nv-ln-table"><div><a href="event_callback.html" title="cpp/io/ios base/event callback"><span class="t-lines"><span>ios_base::event_callback</span></span></a></div></div></td></tr>
</table></div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<table class="t-dcl-begin"><tbody>
<tr class="t-dcl">
<td> <div><span class="mw-geshi cpp source-cpp">streamsize width<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div></td>
<td> (1) </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl">
<td> <div><span class="mw-geshi cpp source-cpp">streamsize width<span class="br0">(</span> streamsize new_width <span class="br0">)</span><span class="sy4">;</span></span></div></td>
<td> (2) </td>
<td class="t-dcl-nopad">  </td>
</tr>
<tr class="t-dcl-sep"><td></td><td></td><td></td></tr>
</tbody></table>
<p>管理某些输出操作时生成的最小字符数，和某些输出操作时生成的最大字符数。
</p>
<div class="t-li1"><span class="t-li">1)</span> 返回当前域宽。</div>
<div class="t-li1"><span class="t-li">2)</span> 设置域宽为给定值。返回先前的位宽。</div>
<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">参数</span></h3>
<table class="t-par-begin">


<tr class="t-par">
<td>  new_width
</td>
<td> -
</td>
<td> 设置的新域宽
</td></tr></table>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">返回值</span></h3>
<p>调用函数前的域宽
</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E6.84.8F">注意</span></h3>
<p>一些 I/O 函数在返回前调用 <span class="t-c"><span class="mw-geshi cpp source-cpp">width<span class="br0">(</span><span class="nu0">0</span><span class="br0">)</span></span></span> ，见 <span class="t-lc"><a href="../manip/setw.html" title="cpp/io/manip/setw">std::setw</a></span> （这导致此域仅在下次 I/O 函数，而不再任何后继 I/O 时有效）。
</p><p>此修改器在输入和输出上拥有的准确效果在单独的 I/O 函数之间有别，效果单独描述于每个 <code>operator&lt;&lt;</code> 和 <code>operator&gt;&gt;</code> 重载的页面。
</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;array&gt;</span>
<span class="co2">#include &lt;tuple&gt;</span>
<span class="co2">#include &lt;ctime&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;sstream&gt;</span>
<span class="co2">#include &lt;iomanip&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">auto</span> str_time <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><span class="kw4">int</span> year, <span class="kw4">int</span> mon, <span class="kw4">int</span> day<span class="br0">)</span>
    <span class="br0">{</span>
        <span class="kw4">constexpr</span> <a href="../../container/array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1">&lt;</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span>, <span class="nu0">7</span><span class="sy1">&gt;</span> week_day<span class="br0">{</span> <span class="br0">{</span>
            <span class="st0">"Sunday"</span>, <span class="st0">"Monday"</span>, <span class="st0">"Tuesday"</span>, <span class="st0">"Wednesday"</span>, <span class="st0">"Thursday"</span>, <span class="st0">"Friday"</span>, <span class="st0">"Saturday"</span>
        <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
 
        <a href="../../chrono/c/tm.html"><span class="kw1023">std::<span class="me2">tm</span></span></a> tm<span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
        tm.<span class="me1">tm_year</span> <span class="sy1">=</span> year <span class="sy2">-</span> <span class="nu0">1900</span><span class="sy4">;</span>
        tm.<span class="me1">tm_mon</span>  <span class="sy1">=</span> mon <span class="sy2">-</span> <span class="nu0">1</span><span class="sy4">;</span>
        tm.<span class="me1">tm_mday</span> <span class="sy1">=</span> day<span class="sy4">;</span>
 
        day <span class="sy2">+</span><span class="sy1">=</span> mon <span class="sy1">&lt;</span> <span class="nu0">3</span> <span class="sy4">?</span> year<span class="sy2">--</span> <span class="sy4">:</span> year <span class="sy2">-</span> <span class="nu0">2</span><span class="sy4">;</span>
        tm.<span class="me1">tm_wday</span> <span class="sy1">=</span> <span class="br0">(</span><span class="nu0">23</span> <span class="sy2">*</span> mon <span class="sy2">/</span> <span class="nu0">9</span> <span class="sy2">+</span> day <span class="sy2">+</span> <span class="nu0">4</span> <span class="sy2">+</span> year <span class="sy2">/</span> <span class="nu0">4</span> <span class="sy2">-</span> year <span class="sy2">/</span> <span class="nu0">100</span> <span class="sy2">+</span> year <span class="sy2">/</span> <span class="nu0">400</span><span class="br0">)</span> <span class="sy2">%</span> <span class="nu0">7</span><span class="sy4">;</span>
 
        <a href="../basic_ostringstream.html"><span class="kw1736">std::<span class="me2">ostringstream</span></span></a> out<span class="sy4">;</span>
        out <span class="sy1">&lt;&lt;</span> week_day<span class="br0">[</span>tm.<span class="me1">tm_wday</span><span class="br0">]</span> <span class="sy1">&lt;&lt;</span> <span class="st0">", "</span> <span class="sy1">&lt;&lt;</span> <a href="../manip/put_time.html"><span class="kw1801">std::<span class="me2">put_time</span></span></a><span class="br0">(</span><span class="sy3">&amp;</span>tm, <span class="st0">"%B %d, %Y"</span><span class="br0">)</span><span class="sy4">;</span>
        <span class="kw1">return</span> out.<span class="me1">str</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="kw4">constexpr</span> <span class="kw4">int</span> column_size <span class="sy1">=</span> <span class="nu0">4</span><span class="sy4">;</span>
    <span class="kw1">using</span> table_t <span class="sy1">=</span> <a href="../../container/array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1">&lt;</span><a href="../../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, column_size<span class="sy1">&gt;</span><span class="sy4">;</span>
 
    table_t headers<span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Name"</span>, <span class="st0">"Birthdate"</span>, <span class="st0">"Death date"</span>, <span class="st0">"Language Created"</span> <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
 
    <a href="../../container/array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1">&lt;</span>table_t, <span class="nu0">5</span><span class="sy1">&gt;</span> data<span class="br0">{</span> <span class="br0">{</span>
        <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Dennis MacAlistair Ritchie"</span>, str_time<span class="br0">(</span><span class="nu0">1941</span>, <span class="nu0">9</span>, <span class="nu0">9</span><span class="br0">)</span>, str_time<span class="br0">(</span><span class="nu0">2011</span>, <span class="nu0">10</span>, <span class="nu0">12</span><span class="br0">)</span>, <span class="st0">"C"</span> <span class="br0">}</span> <span class="br0">}</span>,
        <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Bjarne Stroustrup"</span>, str_time<span class="br0">(</span><span class="nu0">1950</span>, <span class="nu0">12</span>, <span class="nu0">30</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"C++"</span> <span class="br0">}</span> <span class="br0">}</span>,
        <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Anders Hejlsberg"</span>, str_time<span class="br0">(</span><span class="nu0">1960</span>, <span class="nu0">12</span>, <span class="nu0">2</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"C#"</span> <span class="br0">}</span> <span class="br0">}</span>,
        <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Guido van Rossum"</span>, str_time<span class="br0">(</span><span class="nu0">1956</span>, <span class="nu0">1</span>, <span class="nu0">31</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"Python"</span> <span class="br0">}</span> <span class="br0">}</span>,
        <span class="br0">{</span> <span class="br0">{</span> <span class="st0">"Brendan Eich"</span>, str_time<span class="br0">(</span><span class="nu0">1961</span>, <span class="nu0">7</span>, <span class="nu0">4</span><span class="br0">)</span>, <span class="st0">""</span>, <span class="st0">"Javascript"</span> <span class="br0">}</span> <span class="br0">}</span>
    <span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="kw4">constexpr</span> <span class="kw4">int</span> name_wid  <span class="sy1">=</span> <span class="nu0">30</span><span class="sy4">;</span>
    <span class="kw4">constexpr</span> <span class="kw4">int</span> birth_wid <span class="sy1">=</span> <span class="nu0">30</span><span class="sy4">;</span>
    <span class="kw4">constexpr</span> <span class="kw4">int</span> death_wid <span class="sy1">=</span> <span class="nu0">30</span><span class="sy4">;</span>
    <span class="kw4">constexpr</span> <span class="kw4">int</span> lang_wid  <span class="sy1">=</span> <span class="nu0">18</span><span class="sy4">;</span>
 
    <span class="kw4">auto</span> print_line <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span>table_t <span class="kw4">const</span> <span class="sy3">&amp;</span>tbl<span class="br0">)</span>
    <span class="br0">{</span>
 
        <span class="kw4">auto</span> <span class="kw4">const</span> <span class="sy3">&amp;</span><span class="br0">[</span>Name, Birthdate, DeathDate, LanguageCreated<span class="br0">]</span> <span class="sy1">=</span> tbl<span class="sy4">;</span>
 
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">width</span><span class="br0">(</span>name_wid<span class="br0">)</span><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span><span class="st0">"| "</span> <span class="sy2">+</span> Name<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'|'</span><span class="sy4">;</span>
 
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">width</span><span class="br0">(</span>birth_wid<span class="br0">)</span><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span><span class="st0">' '</span> <span class="sy2">+</span> Birthdate<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'|'</span><span class="sy4">;</span>
 
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">width</span><span class="br0">(</span>death_wid<span class="br0">)</span><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span><span class="st0">' '</span> <span class="sy2">+</span> DeathDate<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'|'</span><span class="sy4">;</span>
 
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">width</span><span class="br0">(</span>lang_wid<span class="br0">)</span><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="br0">(</span><span class="st0">' '</span> <span class="sy2">+</span> LanguageCreated<span class="br0">)</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'|'</span><span class="sy4">;</span>
 
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
    <span class="br0">}</span><span class="sy4">;</span>
 
    <span class="kw4">constexpr</span> <span class="kw4">int</span> total_wid <span class="sy1">=</span> name_wid <span class="sy2">+</span> birth_wid <span class="sy2">+</span> death_wid <span class="sy2">+</span> lang_wid <span class="sy2">+</span> column_size<span class="sy4">;</span>
 
    <span class="kw4">auto</span> print_break <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span>
    <span class="br0">{</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">width</span><span class="br0">(</span>total_wid<span class="br0">)</span><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">fill</span><span class="br0">(</span><span class="st0">'-'</span><span class="br0">)</span><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">'-'</span> <span class="sy1">&lt;&lt;</span> <a href="../manip/endl.html"><span class="kw1791">std::<span class="me2">endl</span></span></a><span class="sy4">;</span>
        <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">fill</span><span class="br0">(</span><span class="st0">' '</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="br0">}</span><span class="sy4">;</span>
 
    <a href="../cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a>.<span class="me1">setf</span><span class="br0">(</span>std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">left</span>, std<span class="sy4">::</span><span class="me2">ios</span><span class="sy4">::</span><span class="me2">adjustfield</span><span class="br0">)</span><span class="sy4">;</span>
    print_break<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    print_line<span class="br0">(</span>headers<span class="br0">)</span><span class="sy4">;</span>
    print_break<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> <span class="kw4">const</span> <span class="sy3">&amp;</span>entry <span class="sy4">:</span> data<span class="br0">)</span>
        print_line<span class="br0">(</span>entry<span class="br0">)</span><span class="sy4">;</span>
    print_break<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">----------------------------------------------------------------------------------------------------------------
| Name                        | Birthdate                    | Death date                   | Language Created |
----------------------------------------------------------------------------------------------------------------
| Dennis MacAlistair Ritchie  | Tuesday, September 09, 1941  | Wednesday, October 12, 2011  | C                |
| Bjarne Stroustrup           | Saturday, December 30, 1950  |                              | C++              |
| Anders Hejlsberg            | Friday, December 02, 1960    |                              | C#               |
| Guido van Rossum            | Tuesday, January 31, 1956    |                              | Python           |
| Brendan Eich                | Tuesday, July 04, 1961       |                              | Javascript       |
----------------------------------------------------------------------------------------------------------------</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

<tr class="t-dsc">
<td>  <div class="t-dsc-member-div"><div><a href="precision.html" title="cpp/io/ios base/precision"> <span class="t-lines"><span>precision</span></span></a></div></div>
</td>
<td>   管理浮点操作的精度  <br> <span class="t-mark">(公开成员函数)</span> </td></tr>
</table>

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